The human mutation R192Q (p.R194Q in mouse) was knocked in to exon 4 via homologous recombination along with a floxed neo cassette. Mice carrying both the R194Q and the loxP site flanked neomycin resistance gene cassette were fertile and showed no overt phenotype. The neo cassette was removed through cre-mediated recombination. The presence of the mutation in the resulting animals was confirmed by PCR and restriction enzyme digestion. Semi-quantitative Western blot analysis indicated that the mutant protein was expressed as well as the normal protein.